i just bought a 2000 civic ex with a d16y8 that had an automatic from the factory, but was swapped to a manual at some point. the car runs fine for the most part, but occasionally once it has been running for a while (maybe about 45 minutes to an hour) it will start jerking really bad in first and second around 1500 rpms. the revs will go up and down by a few hundred rpms pretty quickly. there is also a noticeable jerk/jolt that happens at the point of throttle engagement/disengagement. it doesn’t happen every time that i drive, but more often than not. sometimes the jolt at throttle engagement will start after only 15-20 minutes or so. but it seems somewhat random. i checked the throttle body and it moved smoothly from closed to open. i tested my TPS and the voltage on that reads fine and doesn’t have any dead spots. i checked my spark plugs and they all looked okay. the idle air control valve was replaced by the last owner about a week before i bought the car, but it is a three wire IACV and not a two wire that come on manual cars from the factory. the previous owner didn’t swap it to a two pin IACV. the previous owner said he never had this problem. i bought the car to use as a daily for my hour long commute to work, ending in city traffic, so it is pretty annoying having the car jerking while i’m trying to navigate traffic. i am new to working on cars, so any suggestions for what to check/replace/do to try and fix this would be greatly appreciated. the engine has a P0505 code (idle speed control system) and a P0135 code (o2 sensor) which is because the upstream o2 sensor isn’t plugged in (and i can’t find the plug to plug it in on my wiring harness).

 

I have the same issue but i swapped mine to 2 pin and if i plug my plug in the iac it goes off the deep end but i would start with a iac repin